Users receive 5+K to use everyday when logging into their Klout account. This is located on the bottom left hand corner of your account. Users can earn up to 10+K for completing actions on the site. You can never exceed 10+K.
You can use this +K daily to give to other users if they have recently influenced you on a specific topic. To do this, go to the user's topics page and click the “Give +K” button next to the relevant topic. You can also use +Ks to create a topic for yourself or give a topic to others and that will cost 5+K. Gaining +Ks means that you are influential to others about a specific topic and qualifies you for Perks. There is no limit to the amount of +K you can receive from other users.
Learn more: http://corp.klout.com/blog/2011/06/influence-is-topical/